1. Field of the invention
The present invention generally relates to a common rail such as a high pressure fuel manifold in an accumulator fuel injection system of a diesel engine or a block rail.
2. Description of the prior arts
Conventionally, as thick kind of common rail, for example, as shown in FIG. 12, there has been known a common rail of the type which is structured such that a branch hole 21-2 portion communicating with an inner communication passage 21-1 disposed in a peripheral wall portion of a main pipe rail 21 end constituted by a circular pipe is made a pressure receiving seat surface 21-3 open to an outer direction, a cylindrical sleeve nipple 23 is mounted to an outer peripheral wall of the main pipe rail 21 near the pressure receiving seat surface by welding or brazing, and a pressing seat surface 22-3 constituted by a connection head portion 22-2 of a branch pipe 22 is brought into contact and engaged with the pressure receiving seat surface 21-3 close to the main pipe rail 21, thereby fastening and connecting together with pressing under the connection head portion 22-2 neck by means of an engagement between the sleeve nipple 23 and a fastening inside screw nut 24 previously assembled in the branch pipe end. In the drawing, reference numeral 22-1 denotes a flow passage of the branch pipe 22. In this case, the common rail shown in FIG. 12 employs an inside screw type for the screwing means, however, there is a common rail employing an outside screw type.
However, in the case of the common rail of the type that the cylindrical sleeve nipple type common rail which is structured such that the cylindrical sleeve nipple 23 is directly mounted to the main pipe rail 21 by welding or brazing and the nut 24 meshed with the sleeve nipple 23 is fastened and connected, as shown in FIG. 12, a great tensile stress is generated in an inner peripheral edge portion P of a lower end of the branch hole 12-2 due to an axial force applied to the pressure receiving seat surface 21-3 together with the internal pressure of the main pipe rail 21 and the pressing of the connection head portion 22-2 in the branch pipe 22, so that a crack is easily generated with starting from the lower end inner peripheral edge portion P and there is a possibility of inviting a leakage.